Differentiation of the gonads and initiation of mammary gland and scrotum development in the brushtail possum Trichosurus vulpecula (Marsupialia)

Abstract

The first appearance of the mammary and scrotal primordia and the sexual differentiation of the gonads of the brushtail possum, Trichosurus vulpecula, are described. Primordial germ cells were first observed, in fetuses of 7.5 mm crown-rump length, in the gonadal ridges and migrating up the dorsal mesentery. Mammary primordia were first observed in fetuses of 11 mm, and scrotal primordia in those of 12 mm crown-rump length. These structures were diagnostic of female and male brushtail possums respectively. Processus vaginales and gubernacula showed sexual dimorphism, being better developed and appearing earlier in males than in females. Sexual differentiation of the gonads occurred after the appearance of mammary and scrotal primordia, the testes being first recognisable in a 14.5-mm fetus and the ovaries postnatally. Birth occurred between the stages of 14 and 15 mm crown-rump length. These observations appear to indicate that the development of mammary and scrotal primordia are not under gonadal hormonal control, but under direct genetic control, as suggested for the tammar wallaby by previous authors.

A morphometric study of early ovarian development in pouch young of the brushtail possum (Trichosurus vulpecula)

“…However, differentiation and development of the gonads in marsupials occurs postpartum rather than i n utero as in eutherian mammals. In the male young of T. vulpecula, sexual differentiation begins immediately prior to or just after birth, whereas in the female ovarian tissue is not histologically recognisable until a few days after birth (Ullman, 1993). Similar patterns of gonadal differentiation have been reported for other marsupial species, e.g., Isodoon macrorurus (Ullman, 1989), M .…”

“…vulpecula. Previous studies of gonadal differentiation in marsupialia (e.g., bandicoot: Ullman, 1989; brushtail possum: Ullman, 1993; gray short-tailed opossum: Fadem et al, 1992;Maitland and Ullman, 1993) had been restricted to qualitative descriptions of morphological characteristics. The power of stereology has resulted in the present study providing precise information on the pattern of folliculogenesis in the brushtail possum.…”

“…Gonadal initiation, in terms of the origin and migration of primordial germ cells, follows a pattern similar to that seen in eutherians (Tyndale-Biscoe and Renfree, 1987). Primordial germ cells appear along the dorsal mesentery surrounding the hindgut in mid-late gestation and then migrate laterally and emerge in the gonadal ridges dorsal to the mesonephros (Alcorn and Robinson, 1983: Macropus eugenii; Ullman, 1993: T . vulpecula).…”

Oogenesis in the Marsupial Stripe-Faced Dunnart, <i>Sminthopsis macroura</i>

“…In the tammar wallaby, most germ cell migration is completed 1 day before birth [Alcorn and Robinson, 1983;Jiang et al, 1997;Ullmann et al, 1997]. Unlike the bandicoots Isoodon macrourus [Ullmann, 1989], M. domestica [Fadem et al, 1992;Maitland and Ullmann, 1993] and Trichosurus vulpecula [Ullmann, 1993;Frankenberg et al, 1996] in S. macroura the migration of PGC to the indifferent gonad is completed by the day of birth. But like marsupials such as bandicoots [Lyne, 1964] and M. domestica [VandeBerg, 1983] that can come into breeding condition when the female is 3-5 months old and, sometimes in the season of birth, S. macroura exhibits a number of other precocious features of the timetable of oogenesis and folliculogenesis.…”

Morfologia da glândula mamária de gambás da espécie Didelphis sp associada ao modelo marsupial

“…Nos filhotes de idade aproximada de oito dias e tamanho de 2,94 cm já era observado a presença do marsúpio e das papilas mamárias, enquanto que nos machos, já podem ser observados os testículos e o pênis, sendo que Ullmann (1993) relatou que esse dimorfismo sexual já pode ser observado em filhotes com 12 mm (ou 1,2 cm) de comprimento.…”